As a method of crosslinking a fluorinated elastomer to obtain a fluorinated rubber, (1) a method of heating an organic peroxide to form radicals for crosslinking, (2) a method of irradiating a fluorinated rubber with radiation to form radicals for crosslinking, and (3) a method of using a crosslinking agent such as a polyol crosslinking agent or a polyamine crosslinking agent for crosslinking, have been known. Crosslinked rubber articles produced by the methods (1) and (2) are excellent in the chemical resistance (particularly the amine resistance) as compared with a crosslinked rubber article produced by the method (3).
In the methods (1) and (2), in order to improve the crosslinking properties of the fluorinated elastomer and physical properties of the obtainable fluorinated rubber, for example, a polyfunctional compound such as triallyl isocyanurate (hereinafter sometimes referred to as TAIC) is used as a crosslinking aid.
Further, a method of crosslinking and at the same time foaming the fluorinated elastomer to produce a fluorinated foamed rubber (formed product) has been known.
For example, the following Patent Documents 1 and 2 disclose a method for producing a foamed product of a fluorinated rubber by heating a composition comprising a fluorinated rubber (fluorinated elastomer), carbon black, a crosslinking aid, an organic peroxide, an organic blowing agent and thermally expansible microcapsules as a blowing agent, to be foamed and vulcanized. Patent Document 1 relates to a method of heating the composition without pressurizing it at the time of foaming, and Patent Document 2 relates to a method of heating the composition while pressuring it at the time of foaming.
Patent Document 3 discloses a method of heating a composition comprising a fluorinated rubber (fluorinated elastomer), carbon black, an inorganic filler, an organic peroxide, a crosslinking aid, a blowing agent and zinc oxide, to a temperature of at least the decomposition temperatures of the organic peroxide and the blowing agent, to be foamed and crosslinked.
Further, Non-Patent Document 1 discloses a method of forming a foamed product of a fluorinated resin.